You’ll often hear cycads referred to as ‘dinosaur plants’.
And while these slow-growing plants do evoke ideas of giant lizards marching across a verdant world much unlike the one we know today, they aren’t really what you’d find if you powered up your DeLorean and nipped back tens of millions of years.
Cycads are highly genetically diverse with a lineage that dates back 270 million years.
But, strictly speaking, they’re not the same plants that dinosaurs would have chewed on back then.
In May, palaeobotanists from the University of Kansas, US, published a three-dimensional reconstruction of a fossilised cycad cone. This study indicated modern cycads began branching off from their forebears during the Cretaceous period, suggesting a “more dynamic” evolutionary history than had been otherwise assumed.
Dr James Clugston, a botanist from the Royal Botanic Garden Sydney, says labelling modern cycads as living fossils or dinosaur plants ignores the point that, like the dinosaurs themselves and many other plant and animals species over millions of years, cycads have witnessed multiple extinction events.
“Including the K-T extinction event that happened at the end of the Cretaceous period,” says Clugston.
The K-T extinction event, also known as the Cretaceous–Tertiary extinction, eliminated approximately 70-80% of all species of animals about 66 million years ago.
Clugston says: “For something to be a ‘dinosaur plant’, it probably has to be 260 million years old, which is a long time. Cycads, what we know today, have only recently evolved in the last 10 to 12 million years, so they’re still very old, much older than we [humans] are.”
“But their lineage dates back around 270 million years, so they have old ancestry. What we can say is when we see dinosaurs eating plants like cycads, it’s something that probably would have happened to their [cycad] ancestors a long time ago.”
Still, cycads have done a pretty good job at surviving millions of years since.
But they’re not out of the proverbial woods yet: cycads are facing another worldwide extinction event. But rather than a giant asteroid slamming into the Gulf of Mexico, as with the K-T extinction, the causes of this wipeout are anthropogenic.
To understand this, however, we first need to talk about the slowburn romance that is cycad reproduction.
Archaic sex in the time of humans
The cycad lifecycle is a patient one.
“Cycad reproduction is incredibly slow,” says Tim Uebergang, a horticultural team leader and cycad collection curator at the Royal Botanical Gardens of Victoria.
“A great majority of cycads are unlikely to reach sexual maturity in the first ten years of their life in their natural environment and climate change could also be a contributing factor that affects pollinators and plant reproduction.”
While they might not technically be dinosaur plants, cycads were nevertheless among the first modern plants to evolve. They’re gymnosperms – literally ‘naked seeds’ – which, like their conifer cousins, bear their embryos in large, phallic cone structures called strobilus. Compare that to more recently evolved flowering plants – the angiosperms – whose seeds are produced in the plant ovaries which ripen into fruit.
When cycad ancestors shared the planet with dinosaurs, their reproduction was likely facilitated by large megafauna chowing down on the seed cones and distributing them across the land to grow again.
Today, the descendants of ancient cycads and megafauna work together to repeat this process: frugivores like hungry marsupials, birds and megabats chew the edible covering of cycad seeds and discard the reproductive component, usually close to the parent plants. This is why cycads can be found together in large societies which maximise the chance of population growth.
But the slow growth of cycads is fraught with barriers to success. Like humans, plants are either male or female, and not all produce cones at the same time. Whereas an angiosperm might bloom annually for insects to swarm and move pollen from flower to flower, cycad pollinators might wait years for a cone to appear.
That makes the chances of their survival increasingly contingent on other dangers.
Numbers are declining around the world, botanic gardens offer a safe haven
You don’t need to look far in nature to find animals that take a long time to reach sexual maturity and successfully reproduce.
The orange roughy – a tasty deep-sea fish once popular in chippies along the Australian east coast – takes years to grow, hits reproductive age for the first time well into its twenties, and can live for a century. A combination of dinnerplate popularity and poor understanding of its drawn-out breeding timetable saw numbers plummet in the 1980s in the face of overfishing.
On land, the cycad sees not dissimilar threats, but rather than nets through water, it’s tractors across land and fires through their habitats that threatened to uproot and scorch through their numbers.
And, sadly, poaching of rare specimens – some of which earn a five-figure price tag –threatens to consign them to the history books once and for all.
“We’re probably seeing the end of their era,” says Clugston.
“And if we don’t do something to try and conserve these populations, we will eventually lose organisms like this.”
The hope for cycads might lie in botanic gardens. In remote parts of New South Wales, Clugston and fellow botanists from the Royal Botanic Gardens Victoria, Australian Botanic Garden, and Montgomery Botanical Centre in Florida march through dense scrub searching for the rarest of these plants.
When they find an isolated cycad population, they quantify their number and collect DNA for genomic study. This also helps monitoring by authorities like the International Union for the Conservation of Nature’s Red List of threatened species.
Some plants are approved for delicate removal and rehoming in botanic gardens.
Whole plants are preferred because while cycad seeds can be banked, they expire quickly. The best option is to simply stick a plant in the ground.
This enables gardens like those in Sydney, Melbourne, Canberra, Florida and elsewhere to create what Clugston calls “conservation assurance colonies” in different locations. That means a local extinction in one place might not result in the demise of a species.
“It means we can ensure continuous survival and it also means researchers who want to understand these plants have access to them at different sites.”
This global movement of cycad protectors includes botanic gardens as well as government agencies, NGOs, landowners and local communities, according to Uebergang, which will “work in concert to accomplish the long-term conservation of genetically diverse and representative populations of cycads”.
In the meantime, keeping cycads front-of-mind for visitors to botanic gardens might be an important measure for heightening awareness of the conservation dilemma confronting the plants, particularly in Australia.
“We can connect to our audience on a personal level,” says Clugston.
“We can say why these plants are important and by creating ownership of these plants and getting people to care about them, we can conserve these plants into the future.”